(a) Field
The present invention relates to a method and apparatus for transmitting and receiving data, and more particularly, to a method and apparatus for transmitting and receiving orthogonal frequency-division multiplexing (OFDM) data.
(b) Description of the Related Art
An OFDM method is embodied through a simple equalizer, and has strong characteristics in multipath fading and thus in recent wireless communication, the OFDM method has been widely used. The OFDM method is selected and used in several wireless communication systems such as a wireless local area network (WLAN), a wireless metropolitan area network (WMAN), digital audio broadcast (DAB), and digital video broadcast (DVB).
Hereinafter, a conventional OFDM transmitter 10 and OFDM receiver 20 will be described with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram illustrating a conventional OFDM transmitter.
As shown in FIG. 1, the conventional OFDM transmitter 10 includes a serial-to-parallel converter (hereinafter, an SPC) 11, a symbol mapper 12, an inverse fast Fourier transformer (hereinafter, an IFFT operation unit) 13, a parallel-to-serial converter (hereinafter, a PSC) 14, a cyclic prefix inserter (hereinafter, a CP inserter) 15, a digital-to-analog converter (hereinafter, a DAC) 16, a transmitter 17, and at least one transmitting antenna 18.
The SPC 11 converts a plurality of serial binary data signals to a plurality of parallel binary data signals.
The symbol mapper 12 generates a plurality of digital-modulated data symbols by performing digital modulation such as binary phase shift keying (BPSK), quadrature amplitude modulation (QAM), 16-QAM, and 64-QAM on a plurality of parallel binary data signals that are output by the SPC 11.
The IFFT operation unit 13 generates a plurality of inverse-fast-fourier-transformed symbols (IFFT symbols) by performing IFFT on a plurality of digital-modulated data symbols that are outputs by the symbol mapper 12.
The PSC 14 outputs a plurality of IFFT symbols that are output in parallel by the IFFT operation unit 13 in series.
The CP inserter 15 adds a signal of cyclic prefix to a front portion of a plurality of IFFT symbols that are output in series by the PSC 14 and generates a symbol group into which a CP is inserted. Here, a cyclic prefix indicates some symbols of a rear portion of a plurality of IFFT symbols.
The DAC 16 receives a symbol group into which a CP is inserted from the CP inserter 15, converts the symbol group to analog, and generates one OFDM symbol.
The transmitter 17 amplifies and converts an OFDM symbol that is generated by the DAC 16 to a radio frequency (RF) signal and transmits the RF signal to the channel through at least one transmitting antenna 18.
FIG. 2 is a block diagram illustrating a conventional OFDM receiver.
As shown in FIG. 2, the conventional OFDM receiver 20 includes at least one receiving antenna 21, a receiver 22, an analog-to-digital converter (hereinafter, an ADC) 23, a cyclic prefix remover (hereinafter, a CP remover) 24, an SPC 25, a fast Fourier transformer (hereinafter, a FFT operation unit) 26, a symbol demapper 27, and a PSC 28.
The receiver 22 receives an OFDM symbol from a channel through at least one receiving antenna 21.
The ADC 23 converts an OFDM symbol that is received by the receiver 22 to digital and generates a plurality of digital symbols.
The CP remover 24 removes a cyclic prefix from the plurality of digital symbols that the ADC 23 generates.
The SPC 25 receives a plurality of digital symbols in which a CP is removed by the CP remover 24 in series and outputs the plurality of digital symbols in parallel.
The FFT operation unit 26 receives a plurality of symbols that the SPC 25 outputs in parallel, performs fast Fourier transform (FFT), and generates a plurality of fast-Fourier-transformed symbols (FFT symbols).
The symbol demapper 27 generates a plurality of binary data signals by performing digital demodulation such as BPSK, QAM, 16-QAM, and 64-QAM on a plurality of FFT symbols that the FFT operation unit 26 generates.
The PSC 28 converts a plurality of parallel binary data signals that are generated by the symbol demapper 27 to a plurality of serial binary data signals.
However, an OFDM signal generally has a very high average peak-to-average power ratio (PAPR) of about 12 dB in a transmitting terminal, and such a high PAPR causes non-linear distortion in a power amplifier of a transmitter. When not enough backoff is given to electric power, the frequency spectrum of a system is widened and distortion occurs by modulation between frequencies and thus system performance is deteriorated.
A clipping technique and a block coding technique have suggested as methods of lowering a PAPR in an OFDM system. The clipping technique can be easily embodied, but has a drawback that signal quality is deteriorated due to out-of-band radiation and in-band distortion. The block coding technique can limit a PAPR to 3 dB without signal distortion, but has a drawback that as the number of subcarriers increases, a calculation amount exponentially increases and a code rate is greatly deteriorated, and thus spectral efficiency gets worse.
An existing method solves a PAPR problem by compulsorily suppressing a signal of a predetermined size or more in a time domain, and thus a distortion phenomenon of an OFDM signal occurs.